Specific parts of a creature can’t be singled out. Inanimate objects are still damaged by the spell however.

For every two caster levels beyond 1st, you gain an additional missile—two at 3rd level, three at 5th, four at 7th, and the maximum of five missiles at 9th level or higher. If you shoot multiple missiles, you can have them strike a single creature or several creatures. Regardless of the number of missiles fired, you only make one Reflex save. A single missile can strike only one creature. You must designate targets before you check for spell resistance or roll damage.